1. Field of the Invention
The present invention relates to osseodontic dental implant systems for tooth replacement in orthodontic patients.
2. Description of the Prior Art
In the field of orthodontics there are several techniques for tooth replacement. Crowns are widely employed for this purpose. However, dental crowns require a sturdy foundation. In the simplest, most desirable and least costly procedure the natural structure of the root of a tooth is utilized as the foundation to which the crown is anchored. However, in some instances, this is impractical since a tooth may be so badly damaged due to disease or injury that the entire tooth must be removed.
In such a situation one option is the use of an endosseous dental implant system. In such a system an implant member is inserted into the jaw of a patient. Very typically the implant member will be externally threaded with self-tapping screw threads that anchor the implant member into the bone of the jaw underlying the patient's gums. The implant member may be internally tapped to receive a screw.
The implant member has opposing gingival and osseous ends. That is, the implant member is of a generally cylindrical, externally threaded configuration with an internally tapped blind bore therein. The open end of the bore is at the gingival end of the implant member which resides at the patient's gum when the implant member is installed. The opposite, osseous end penetrates into the bone structure of the patient's jaw.
A conventional osseous dental implant system also includes an abutment member. The abutment member also has opposing ends which may be referred to as the gingival and coping support ends. The gingival end of the abutment member faces and mates with the gingival end of the implant member. The abutment member includes an internal, longitudinal bore with openings at both of its ends and with a bearing ledge defined within its structure. A coping, which is an artificial tooth or crown, is ultimately permanently attached to the coping support end of the abutment. A screw is utilized to attach the abutment member to the implant member. The externally threaded shank of the screw extends through the longitudinal bore through the structure of the abutment member and is threadably engaged with the internal threads of the blind, tapped bore in the implant member. The head of the screw rests upon the bearing ledge in the structure of the abutment member to firmly, and ultimately permanently, attach the abutment member to the implant member.
It is extremely important for the abutment member to be totally immobilized relative to the implant member. In early systems one difficulty that occurred was that the abutment member would twist relative to the implant member, thus creating angular misalignment of the artificial tooth about the axis of the fastening screw. To remedy this problem the implant member and the abutment member were fashioned with a socket of noncircular cross section in one of the members and a post of corresponding noncircular cross section in the other of the members. When the abutment member is placed in face-to-face contact with the implant member, the gingival ends of both members mate with each other. That is, the post enters the socket in snug fitting relationship therewith.
The post and socket are both of corresponding noncircular cross section, typically polygonal in shape. For example, both the post and socket may have a hexagonal cross section. Because the post and socket are both of noncircular shape, it was thought that the abutment member could be completely immobilized from any rotational movement relative to the implant member.
However, certain difficulties with this prior system occurred. Specifically, due to the necessary dimensional tolerance that must exist for a post to be inserted into a socket, conventional implant and abutment systems of the type described still experience some slight twisting of the abutment member relative to the implant member. To eliminate this, another system was devised. Specifically, the mating polygonal post and socket arrangement was modified so that the post was tapered downwardly in a convergent manner in a direction toward the abutment. That is, the cross section of the post was configured to have a progressively reduced cross-sectional area proceeding from its base toward its distal extremity that was inserted into the abutment member. While this arrangement did address the problem of rotation of the post relative to the socket, it creates another problem in that it is possible for an interstitial gap to exist between the faces of the gingival ends of the implant and socket members surrounding the socket opening and the post. On the other hand, it is also possible with such a construction for the post to fail to reach the bottom of the socket, thereby creating a cavity into which fluids in the patient's mouth can seep.